Method for controlling a combustion and/or gasification device

ABSTRACT

Combustion and/or gasification devices for the thermal utilisation of different solid fuels, and a method for controlling a combustion and/or gasification device for small-size solid fuels with throw-feeding. A combustion and/or gasification device includes at least one combustion or gasification chamber and a grate with at least two grate zones which are arranged in a longitudinal direction of the grate. A glowing fire edge is formed in one of the grate zones, especially in the so-called burnout zone.

BACKGROUND OF THE INVENTION

The present invention generally relates to the field of combustion and/or gasification devices, especially for the thermal utilisation of different solid fuels. The present invention especially relates to a method for controlling a combustion and/or gasification device for small-size solid fuels with throw-feeding. A combustion and/or gasification device comprises at least one combustion or gasification chamber and a grate with at least two grate zones (e.g. a combustion or gasification zone as a first zone and a burnout zone as the second zone), which are arranged in the longitudinal direction of the grate. A so-called glowing fire edge is formed in one of the grate zones, especially in the so-called burnout zone.

DESCRIPTION OF THE PRIOR ART

Combustion and/or gasification devices for the thermal utilisation of different solid fuels are used for example for cogeneration in the industrial field and/or by local communities. Residual matter (e.g. wood, rejects, fibrous paper material, conditioned waste, dried sewage sludge, special (ecological) fuels etc) is used for example as solid fuels, which would otherwise be disposed of as waste in waste incineration plants. Such devices are used for example in the paper industry for producing electrical power and/or steam for drying cardboard, by local authorities for generating sustainable power from biomass waste or for the disposal of sewage sludge from sewage plants or in installations for the incineration gasification of biomass.

The combustion or gasification of solid fuels, which are introduced into the combustion or gasification device for example in small-sized form by way of introduction by throwing (i.e. so-called throw-feeding), usually occurs on a grate. During throw-feeding the mostly small-size solid fuel is introduced by means of a so-called throw-feeder or throw-wheel into a combustion or gasification chamber, and it is thus distributed evenly over the grate.

At least two zones are formed on the grate, which are arranged in the longitudinal direction of the grate. A so-called combustion zone or gasification zone is thus produced, which assumes approximately ⅘ of the grate area, and a so-called burnout zone, which assumes ⅕ of the grate area. The combustion or gasification zone is characterized by constant combustion over a large area. The fuel is incinerated or gasified in said zone from the top to the bottom. New fuel is regularly introduced by scattering into the zone, which drops into a burning environment and ignites immediately. No fuel is thrown onto the burnout zone. The burnout zone is thus characterized by a so-called glowing fire edge, after which the glowing fire extinguishes, wherein the temperature and the colour of the ash after the glowing fire edge decrease rapidly. Only the burnout of the ash occurs there, which is then discharged to a so-called ash discharge.

A control of such a combustion or gasification device occurs in form of feedback control of a supplied air quantity, e.g. in form of so-called primary, secondary and tertiary air. An air quantity to be introduced is controlled for example depending on a power requirement, a water content of the fuel and measured reaction parameters (e.g. temperature above the grate, temperature at the end of the burnout zone etc). In addition, a ratio of the so-called primary air to a so-called primary recirculation air quantity and to a so-called secondary recirculation air is additionally controlled by means of these parameters. The so-called primary air is understood to be the air quantity which is supplied directly beneath a grate zone. In a combustion or gasification device (such as a bed gasification device for example), the supply of the primary air usually occurs from beneath the grate and thus has a relevant influence on the combustion or gasification on the grate and thus on the burnout. The so-called secondary air is usually supplied from above and is used for a so-called post-oxidation of the gases produced on the grate for example. The recirculation air quantity is understood to be the quantity of exhaust gases or flue gases (e.g. from introduced primary air etc) by means of which combustion or gasification processes can be further optimised by means of recirculation. The entire air quantity (e.g. primary air, primary recirculation air) for the feedback control of the combustion or gasification can be emitted in this process in a single zone beneath the grate for example. It is also possible to introduce the air (e.g. primary air, primary recirculation air) specific to the zones. If the grate is physically subdivided in the longitudinal direction into at least two zones for example, these zones can be supplied separately with such air.

The feedback control of the air supply intends to achieve constant combustion conditions in the combustion zone or constant gasification conditions in the gasification zone of the grate and complete burnout of the ash (e.g. a residual carbon content of less than 1%). The respective feedback control of the air supply further intends to prevent that glowing ash is conveyed into the ash discharge. In order to prevent conveyance of glowing ash into the ash discharge, continuous monitoring and control of a position of the glowing fire edge is necessary. Such control of the glowing fire edge is currently performed manually for example. This means the position is monitored by the operators during regular inspections for example and the supply of air is then readjusted according to the position of the glowing fire edge. Such a procedure is very cumbersome, work-intensive and optionally imprecise because the operators need to monitor the glowing fire edge precisely and respective measures need to be initiated partly in a manual way, wherein the glowing fire edge needs to be checked again precisely.

In the case of conventional grate combustion or grate incineration, in which the fuel is introduced via a slide-in system for example and is incinerated on the grate (usually without formation of a specific glowing fire edge), systems for monitoring the combustion chamber are used. In the case of these systems, the fuel needs to be heated first before it will ignite approximately in the middle of the grate and will start to burn. Locally high temperatures occur as a result of the combustion in the relatively narrow space, as a result of which large amounts of slag are formed on the grate, which slag - which is still partly glowing in its interior - is then quenched in a water bed in the slag discharge.

In the case of these systems, a temperature profile is measured over the grate by means of a thermal camera (e.g. via infrared measurement) and respective feedback control processes, especially for local air supply, are derived from this temperature profile. These systems come with the disadvantage however that such thermal or infrared cameras are relatively expensive and their use is very complex, especially for determining or controlling the glowing fire edge position, since a position of the glowing fire edge needs to be derived from the temperature profile by means of a respectively complex follow-up treatment.

So-called furnace-chamber or combustion-chamber cameras can further be used in industrial incineration devices such as waste incineration plants for monitoring the temperature distribution or flame image and thus a glowing fire edge. A glowing fire edge can be determined by means of such combustion-chamber cameras via respective evaluation units, or it can be determined whether the glowing fire edge is situated within a target area. Such cameras are (infrared) cameras which are especially arranged for the conditions in an incineration device. The use of such (infrared) cameras for determining the glowing fire edge position is expensive and requires much effort however.

SUMMARY OF THE INVENTION

The invention is therefore based on the object of providing a method for controlling a combustion and/or gasification device for solid fuels, in which a position of a glowing fire edge can be determined in a simple and cost-effective way and is used for respective control.

This object is achieved by a method of the kind mentioned above in which an actual position of the glowing fire edge is monitored with at least one optical camera. In the case of a deviation of the actual position of the glowing fire edge from a target position, a controlled change in the air supply, especially a so-called primary air quantity and/or a so-called primary recirculation quantity, is carried out in a combustion chamber of the combustion or gasification device.

The main aspect of the solution proposed in accordance with the invention is that an actual position of the glowing fire edge is determined in a simple way. Depending on the determined actual position of the glowing fire edge or the deviation of the glowing fire edge from the target position, a respective change in the air supply is carried out. In this process, the entire air supply (i.e. primary and primary recirculation air quantity) can be increased or decreased, or it is also possible to perform a decrease in the primary air quantity in combination with an increase in the recirculation air quantity, or an increase in the primary air quantity in combination with a decrease in the recirculation air quantity, in order to shift the fire glowing edge in the direction towards the target position. As a result, a burnout of the ash is thus automated in a simple and cost-effective manner, the air quantity respectively required for this purpose (e.g. primary air, recirculation air) is optimised and a complete burnout of the ash (e.g. residual carbon content of less than 1%) is ensured. It is additionally prevented that glowing ash can reach the ash discharge. The method in accordance with the invention allows the combustion device to respond automatically to changing burnout properties due to changing fuel properties for example.

The optical camera can be introduced into the combustion chamber of the combustion or gasification device for shooting images for determining the actual position of the glowing fire edge. An optimal visual angle is achieved in this manner, in which simultaneously it is possible to make a recording of flames, the glowing fire edge and the grate in the combustion and gasification device. The optical camera thus easily supplies meaningful pictures or snapshots of a combustion chamber of the combustion or gasification device for evaluating or determining a glowing fire position. The camera or the optics for the snapshot can ideally be housed in an especially cooled housing or be provided with a cooling system in order to prevent damage by heating or by the heat.

It is alternatively also possible to attach the camera outside of the combustion chamber of the combustion or gasification device. It can be advantageous if a snapshot of the glowing fire edge is made through one of the so-called inspection holes, especially through the inspection hole in a so-called firebox door. The optical camera is attached to a tripod outside of the combustion chamber for example. In the case of snapshots through an inspection hole (e.g. in the firebox door), a visual angle is achieved by the camera in which it is possible to simultaneously perform a snapshot of the flames, the glowing fire edge and the grate.

Since ash deposits can occur in the inspection holes of the combustion or gasification device, through which snapshots can be obstructed, a compressed-air nozzle can be used for maintaining the visual field of the optical camera. The compressed air can be used to clean a window of the inspection hole from ash through which snapshots are made with the camera and visual obstructions by ash for example can be remedied in a very simple way.

A processor is ideally used for image analysis which is connected to the camera. The camera can thus be programmed in a very simple way by means of respective software for image analysis and thus for determining the glowing fire edge position. The connection of the processor with the camera can be arranged depending on the position of the camera for example. If the camera is housed or introduced into the combustion chamber, the processor can be arranged outside of the combustion chamber or outside of the combustion or gasification device. If the camera is situated outside of the combustion chamber of the combustion or gasification device, the processor can be integrated in the camera for example.

An appropriate further development of the method in accordance with the invention provides that the analysis of the snapshots and thus an analysis of the actual position of the glowing fire edge are carried out by means of so-called colour evaluation. During the so-called colour evaluation, small sections of the image of a snapshot are analysed and a colour difference to previously defined reference colours is output. A position of the glowing fire edge can be determined for example in this manner through the different colour values in the combustion chamber of flames, the glowing fire edge, the grate etc.

It is advantageous if virtual sensors are used for colour evaluation, of which at least three states, especially a glowing fire state, a warning state and an error state, are assumed depending on the determined actual colour values, and which sensors are arranged in rows.

The virtual sensors, which are also known as soft sensors, are sensors that are realised by means of software. The virtual sensors in the camera processor can be realised very easily by means of programming in the camera or for image evaluation. Values are measured and calculated by virtual sensors which are derived from the measured values of real sensors by means of an empirically acquired or physical model. Virtual sensors are ideally used in applications in which real sensors are either too expensive or are unable to withstand ambient conditions for example (e.g. heat of the combustion device, dust loading by ash etc), or which would wear off too rapidly. Colour evaluation of the snapshots of the camera and a determination of the glowing fire edge can thus be performed in a simple and cost-effective way.

An appropriate embodiment of the method in accordance with the invention provides that the actual colour values of small image sections are compared by the virtual sensors with predetermined reference colour values for said image sections, that thereupon the respective sensor is set to an error state upon exceeding a freely definable threshold value by a colour difference between an actual colour value and a reference colour value, and that an actual position of the glowing fire edge is determined by evaluating the individual sensor states. These sensor states can be evaluated in a very simple manner by means of a check program and a current glowing fire edge position can be derived therefrom. Especially by arranging the virtual sensors in rows, the glowing fire edge position is can be associated to the rows of sensors for example, which can then be output by the check program for example.

BRIEF DESCRIPTION OF THE DRAWING

The invention will be explained below schematically by way of example by reference to the enclosed FIG. 1. FIG. 1 schematically shows an exemplary sequence of the method in accordance with the invention in an exemplary combustion or gasification device for small-size solid fuels with throw-feeding.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 1 schematically shows an exemplary combustion or gasification device VB for solid small-size fuels BS, which is set up for performing the method in accordance with the invention. The device VB comprises at least one combustion chamber BK and a grate R, on which combustion or gasification of the fuels BS is performed. The fuels BS are injected into the combustion chamber BK for combustion or gasification by means of so-called throw-feeder WB and thus evenly distributed on the grate R.

The grate R, on which the fuels BS to be incinerated and the ash A are situated, can be subdivided into at least two grate zones, which are arranged in the longitudinal direction of the grate R. Such grate zones are especially a so-called combustion or gasification zone which assumes approximately ⅘^(th) of the grate area for example, and a so-called burnout zone which comprises approximately ⅕^(th) of the grate zone. The combustion or gasification zone of the grate R is characterized by the combustion or gasification of the fuels BS over a large area, which are combusted from top to bottom and are repeatedly restocked by the throw-feeder WB simultaneously. No fuels BS are supplied to the burnout zone. The burnout zone is therefore characterized by a so-called glowing fire edge GK. The embers extinguish at this glowing fire edge GK, the temperature decreases rapidly and the colour of the ash A changes, because only burnout and cooling of the ash A occurs there. The burnt-out ash A is then conveyed to an ash discharge AS.

Control of the combustion or gasification device VB occurs in form of feedback control of an air supply LV1, LV2 depending on input parameters such as performance specifications, water content of the fuel, combustion parameters etc, wherein it is possible to distinguish between primary PL1, PL2, secondary and optionally tertiary air, wherein a supply of the primary air PL1, PL2 occurs directly for combustion or gasification from beneath the grate R. Temperature values can be measured in the combustion chamber BK at different temperature measuring points T as reaction parameters, as shown in FIG. 1 above the grate R in the combustion/gasification zone or in the burnout zone, in an exhaust gas outlet AB etc. The input parameters are also used for controlling a ratio of primary air PL1, PL2 to a so-called primary recirculation air RL1, RL2 and to a so-called secondary recirculation air.

Only a primary air supply PL1, PL2 and a primary recirculation air RL1, RL2 are shown for reasons of simplicity in the combustion or gasification device VB as illustrated in FIG. 1 by way of example, which are controlled by means of the method in accordance with the invention.

The entire air supply LV1, LV2 with primary and recirculation air can be supplied for example to a single zone beneath the grate R in a combustion or gasification device VB with a throw-feeder WB. In further developed combustion or gasification devices VB (as in the device VB shown by way of example in FIG. 1), the at least two zones such as combustion/gasification zone, burnout zone etc are supplied separately with air. The combustion or gasification zone is supplied with a via a first air supply LV1, consisting of a first primary air PL1 and a first recirculation air RL1. A second air supply LV2 with a second primary air PL2 and a second recirculation air RL2 is used for the burnout zone. A respective feedback control of the air supply LV1, LV2 prevents that glowing ash A reaches the ash discharge AS. This means that a position of a glowing fire edge GK needs to be controlled continuously.

At least one optical camera K is provided for such monitoring. This camera K is used to carry out snapshots of the combustion chamber BK, especially the glowing fire edge GK, in a first method step 1 through one of the so-called inspection holes of the combustion device VB. A current or actual position of the glowing fire edge GK is thus monitored continuously. Changes in the actual position of the glowing fire edge GK can thus be determined in a very simple way. The camera K can be fixed to a tripod or introduced into the combustion chamber BK for example for taking the snapshots.

If the camera K is attached outside of the combustion chamber BK for example, snapshots can be taken through a so-called inspection hole, especially the inspection hole in the so-called firebox door. Said inspection hole offers a suitable visual angle on the flames, the glowing fire edge GK and the grate R in order to evaluate the current or actual position of the glowing fire edge GK. In order to enable snapshots through a window of an inspection hole, the visual field of the camera K must be kept free from ash deposits, dust particles etc. A compressed-air nozzle is used for this purpose for example. In the case of permanent use, the camera K must be provided with a cooling system because heating of the camera K and damage thereto can occur as a result of the strong thermal radiation of the combustion or gasification device VB.

It is alternatively possible to introduce the camera K into the combustion chamber BK of the combustion or gasification device VB. The camera K is protected for this purpose by a specially cooled housing or a cooling system for example. An optimal and sufficiently large visual angle for recording flames, the glowing fire edge GK and the grate R is enabled by introduction into the combustion chamber BK or into the incineration chamber, which allows an even better evaluation of a glowing fire edge position than a visual angle through an inspection hole.

It is determined in a second method step on the basis of the snapshots whether or not and the extent to which the actual position of the glowing fire edge GK deviates from a target position. The camera K may comprise an integrated processor P for an analysis of the snapshots for example if it is attached outside of the combustion chamber BK. If the camera K is introduced into the combustion chamber BK, the processor P (as shown in FIG. 1 by way of example) is attached separate from the camera K outside of the combustion chamber BK and is connected to the camera K. It is further also possible that the camera K and/or the processor P are connected via a network connection (e.g. a network cable) to an evaluation and/or output unit (e.g. a personal computer etc), via which the glowing edge GK can be monitored continuously by the operators of the combustion or gasification device VB.

A so-called colour evaluation is used for the analysis of the snapshots and therefore the actual position of the glowing fire edge GK in the second method step 2. Small image sections, especially the colour values of said image sections, of the respective snapshots are analysed by means of virtual sensors. The virtual sensors are ideally arranged in rows, wherein a glowing fire edge position can be associated with each row, which can then be output or displayed to the operators. The target position of the glowing fire edge GK can be predetermined for example by defined reference colour values for the respective positions of the virtual sensors.

A virtual sensor can assume three states for example: a positive state when the analysed image colour value corresponds to a predetermined reference colour value, a warning state when a colour difference from a previously defined reference colour value has occurred, but which still lies within a defined limit or beneath a freely definable limit value for example, and an error state when the colour difference from a previously defined reference colour value has risen above the freely definable limit value. The current actual position of the glowing fire edge GK or a deviation of the glowing fire edge GK from the target position can be determined in the respective snapshot by an evaluation of the respective sensor states (e.g. via a check program etc). Changes in the actual position of the glowing fire edge GK (e.g. the direction in which the glowing fire edge is moved etc) can be determined by analysing several snapshots taken successively by the camera K.

In addition, the virtual sensors must also consider fluctuating brightness caused by brief flaring in the combustion chamber BK, so that an error state is not erroneously output by the virtual sensors. In order to prevent this, different tolerance ranges can be set for example for different fuels BS (e.g. wood, rejects, fibrous paper materials, conditioned waste, dried sewage sludge, special (ecological) fuels etc). In addition, it is possible to prevent by means of a buffer in the output of the determined fire edge position that flaring will distort the result of the image analysis or that a wrong actual position of the glowing fire edge GK is output. As a result of the buffer, values or changes in the glowing fire edge position are only accepted after a longer definable period of time. This means that an actual position of the glowing fire edge GK will only be output by the buffer for example when a specific state (e.g. error state, positive state etc) is applied to the respective virtual sensors for a specific period of time (e.g. a few minutes).

A controlled change in the air supply via the air supply LV1, LV2 to the combustion chamber BK is performed in a third method step 3 depending on a deviation of the glowing fire edge GK from the target position or as a result of established changes in the actual position of the glowing fire edge GK. Changes are made especially to the primary air or the primary air quantity PL1, PL2 and/or the primary recirculation air (quantity) RL1, RL2, which are supplied from beneath the grate R.

If it is determined in the second method step 2 during the analysis for example that the glowing fire edge GK moves away from the camera K in the direction towards the combustion or gasification zone, the primary air quantity PL1, PL2 is reduced in the third method step 3 for example and the recirculation air quantity RL1, RL2 is increased. If it is determined in the second method step 2 however that the glowing fire edge GK moves in the direction towards the ash discharge AS (i.e. towards the camera K), the primary air quantity PL1, PL2 is increased in the third method step 3 and the recirculation air quantity RL1, RL2 is decreased. If the analysis of snapshots in the second method step 2 determines for example that the glowing fire edge GK remains stable but is not situated in the target position, the total air quantity (primary and reduction air) PL1, PL2, RL1, RL2 can be decreased in the third method step 3 when the glowing fire edge GK is displaced in the direction towards the combustion or gasification zone, or the total air quantity (primary and reduction air) PL1, PL2, RL1, RL2 is increased and in addition an advancing motion of the grate R is decelerated when the glowing fire edge GK is displaced in the direction towards the ash discharge AS. Intervention in the air supply LV1, LV2 of the combustion device VB will not occur only when the snapshots show that the glowing fire edge GK is situated at the target position.

A respective intervention in the air supply LV1, LV2 in the third method step 3 prevents that glowing ash will reach the ash discharge AS, thereby reducing the temperature load on the discharge devices. In addition, complete burnout of the ash A is ensured and the combustion device VB is able to respond automatically to changing burnout properties as a result of changing fuel properties for example. A so-called glowing fire tongue can further be recognised by respective logic changes/adaptations in the evaluation of snapshots or the respective sensor states (e.g. via a check program etc), which can occur for example in combustion or gasification devices VB with more than one throw-wheel in the throw-feeder WB.

LIST OF REFERENCE NUMERALS

VB Combustion or gasification device

AB Exhaust gas outlet

BK Combustion chamber

BS Fuels

WB Throw-feeder

K Camera (optical)

P Processor for image analysis

GK Glowing fire edge

R Grate

A Ash

LV1 Air supply of the combustion zone

PL1 Primary air for the combustion zone

RL1 Primary recirculation air for the combustion zone

LV2 Air supply of the burnout zone

PL2 Primary air for the burnout zone

RL2 Primary recirculation air for the burnout zone

AS Ash discharge

T Temperature measuring points

1, 2, 3 Method steps of the method in accordance with the invention 

1-5. (canceled)
 6. A method for controlling a combustion device for small-sized, solid fuels with litter feed, the combustion device having at least one combustion chamber and a grid with at least having a pair of grate zones which are arranged in a longitudinal direction of the grid, the method comprising: forming a Glutkante in one of the grating zones; monitoring an actual position of the Glutkante; and carrying out a regulated change in an amount of an air supply in the combustion chamber for a deviation of the actual position of the Glutkante relative to a target position. in particular an amount of primary air so-called (PL1, PL2) and/or so-called primary recirculation (RL1, RL2) in the combustion chamber (BK) is carried out (2, 3)
 7. The method of claim 6, wherein the monitoring of the actual position of the Glutkante is conducted with at least one optical device.
 8. The method of claim 7, wherein the at least one optical device comprises an optical camera.
 9. The method of claim 6, further comprising analyzing the actual position of the Glutkante via a processor connected to an optical device.
 10. The method of claim 9, wherein the analysis of the actual position of the Glutkante is conducted via color evaluation.
 11. The method of claim 10, wherein the color evaluation is conducted via virtual sensors.
 12. The method of claim 11, wherein the virtual sensors conduct the color evaluation based upon a good condition, a warning condition and a fault condition.
 13. The method of claim 12, further comprising comparing actual color values smaller image segments with predetermined reference color values for the image sections using the virtual sensors that then at exceeding of a freely definable definable threshold value by a color difference between the actual color value and the reference color value the corresponding sensor is placed in the error state, and then determining by an evaluation of the individual sensor states an actual position of the Glutkante. 